1. Field of the Invention
The invention relates to instruments which can electronically produce a purality of tones, the characteristics of such tones being selectable.
2. Prior Art
A coventional organ can have several keyboards which are referred to as manuals. Each manual has typically sixty-one keys with span five octaves. Associated with each manual are several groups of pipes which are referred to as ranks of pipes. The pipes in these ranks correspond to the keys in the associated manual, so that there are typically sixty-one pipes in ranks associated with a sixty-one key manual. Additionally a pedal manual with 30 or 32 keys is provided to be played by the performer's feet.
The ranks played by any one manual are selected by manual controls referred to as stops. There is normally one stop for each rank, and, in some cases, there are stops which control a group of ranks.
It is frequently desirable to play from one manual ranks associated with another manual. Equipment to perform this function are referred to as intermanual couplers. These couplers can intercouple manuals so that actuation of a key plays pipes associated with the corresponding key on the other manual. These couplers can also be arranged so that actuation of a key in one manual plays pipes associated with an octavely related key in the other manual. The difference can be chosen as one or more octaves. If the coupled key is of a higher or lower note, this is referred to as superoctave or suboctave coupling, respectively.
It is also frequently desirable to couple together keys of the same manual so that actuation of one key operates octavely related keys in the same manual. If the additional key coupled in this fashion is an integer number of octaves higher of lower, this is referred to as superoctave or suboctave intramanual coupling, respectively.
An organ may have a celeste rank which is slightly mistuned from the other ranks. These celeste ranks, if played alone, would appear to have the same pitch as the other basic ranks, but when played together, the slight mistuning causes a noticeable beating effect.
An organ also has ranks whose corresponding pitches are substantially different from the basic rank (referred to in the art as an eight foot rank). These other ranks bear a harmonic relation to the basic ranks.
Ranks are also classified by the construction of their pipes, e.g. diapason, flute, string, reed etc. These classes are aurally distinct in that each has a unique harmonic richness and a unique attack (attack being the manner in which the amplitude of the tone increases).
Known electronic organs have used separate oscillators for each key of a manual. This approach has practical disadvantages for organs having more than several stops since the required number of oscillators is the product of the number of notes and stops. Known techniques for reducing the number of oscillators include synthesizing a plurality of frequencies from a series of frequency dividers. However, this approach establishes a fixed phase coherence between notes so that chords have a relatively flat or lifeless quality.
Other known electronic organs have tried to minimize the number of independent oscillators by providing an n x m matrix of oscillators, with n being the number of notes in an octave and m the number of octaves in the manual. The m array of oscillators are distributed at octave spacings with the lowest frequency being at a supersonic frequency F. The n array of oscillators have frequencies which exceed F by amounts corresponding to the frequencies which are to be produced by the lowest octave of the manual. A selected pair from the m and n arrays are mixed to produce an audio frequency. Because one oscillator from the n array must produce m different notes, these notes must be derived from m different harmonics of that oscillator. Using different harmonics in this fashion will produce audio signals whose magnitudes can vary depending on the harmonic utilized. Moreover, the phasing of frequency components within the audio signal so produced will vary with different such harmonics.
Another disadvantage with an n x m matrix is that each additional voice requires an additional array of m oscillators. A further disadvantage is that intermanual and intramanual coupling is extraordinarily difficult to perform with an n x m matrix.
Other known systems use digital memories, each having stored therein successive values of a waveshape representing a desired voice. The number of memories, however, is multiplied by the number of voices desired. Also, additional circuitry is required to allow simultaneous actuation of different notes. In particular, circuitry is required to allow a memory to provide separate data outputs at different data rates. An example of a system of the latter type is shown in U.S. Pat. No. 3,515,792.